Nutrient Uptake Experiment

Title: Nutrient Uptake Experiment

Overview

This experiment uses hands-on methods to demonstrate how quickly available nutrients are absorbed by algae, and will give students an idea of how quickly an algal bloom can occur. It can also be used to explain nutrient cycling, as students see the nutrients go from available form to organic form.

Most field tests for nutrients detect only available forms of nutrients. For phosphorus, the available form is orthophosphate. For nitrogen, there are typically three different tests for the three basic forms that available nitrogen can take – ammonia (NH3), nitrite (NO2) and nitrate (NO3). These numbers are added together to get total available nitrogen.[1]

In aquatic environments, nutrients do not stay in available form for very long. They are quickly taken up by aquatic plants. Algae typically

outcompete other aquatic plants for available nutrients, and are able to absorb large amounts of nutrients, which is why we see an explosion (or "bloom") of algae in water systems that have recently had a large input of nutrients. As nutrients are taken up by algae and other plants, they are converted to organic form. The nutrients are still present in the aquatic system, but are no longer detectable by the tests for available forms. If someone would like to test a stream or lake to find out how many nutrients are being washed off the land into the water, it is important to collect the sample during the peak of a runoff event. This allows them to measure the nutrients before they are taken up and converted to organic forms.

Tests for nutrients in organic form do exist, but they are typically expensive and more complicated than tests for available forms.

Grades: High School

Learning Objective

Demonstrate that algae quickly soak up available forms of nutrients, and demonstrate that nutrients change forms as they cycle through the environment.

identify an environmental topic to be studied using primary and secondary sources of information, and pose a research question or hypothesis, identifying key variables.

Example: Select a river or stream to investigate for water quality. Have the students go to various sources (libraries, government agencies, the Internet, etc.), collect information (from books, journals, pamphlets, etc.) and write a review of literature (with citations) regarding water quality issues. variables; develop hypotheses; collect, organize and analyze information/data through surveys, interviews, experiments, or other means.

2. select appropriate measurement strategies, which may include models and simulations.

3. collect data through surveys, interviews, experiments, or other means.

4. consider relationships among variables, develop insightful interpretations, and examine evidence for support or non‑support of the hypothesis.

Example: Identify a local environmental issue that can be tested using science process skills. Develop an open-ended problem question and design and conduct an investigation to test the question. E.g., investigate the effects of XYZ sewage treatment plant on ABC Creek. After completing the investigation, evaluate the processes used and the reliability of the results.

Materials

A large Mason jar or other container, preferably clear glass.

Algae (relatively easy to find in ponds and small streams)

Fertilizer or other nutrient source. Most common plant fertilizers list available nutrients on the container. We have found that Osmocote brand works well, though they are time-release pellets and must be crushed to a fine powder for this experiment. The goal is for nutrients to be taken up rapidly, so whatever fertilizer you use must dissolve rapidly in water (liquid or fine powder).

Important Note! Avoid Miracle Grow, or any other product that might turn the water a different color. Miracle Grow turns the water blue, which interferes with the results of the phosphate test.

Phosphorus test kit** Nitrogen test strips** Ammonia test strips**

**This experiment may be done using any combination of these tests. For example, if your students are only discussing phosphorus, it is not necessary to include the nitrogen and ammonia tests.

Method

1. Fill the Mason jar with water from your pond or stream source. Try to let some algae flow into the jar along with the water. If the algae are

attached to a rock or other substrate, it is ok to pick it with your hands and place it in the jar. Use your best judgment about putting your hands in the water if your source seems heavily polluted.

*Remember that it is good to triple-rinse the jar before collecting the sample. Fill the jar with sample water, swirl or shake, and dump the water downstream or in an area away from where you are collecting your sample to avoid contamination. Repeat three times, then collect the final sample.

2. Perform a preliminary test of the nutrient levels in the jar. Unless there was a recent runoff event, they will most likely test at or near 0 ppm (see the phosphorus and nitrogen lessons for directions on using the nutrient tests).

3. Add a small sprinkle of plant fertilizer to the mason jar. It takes only a small amount to get the desired results, and if you add too much the algae may not be able to take up enough to see a difference very quickly.

4. Stir the contents well by swirling the jar. It is not necessary to shake the jar.

5. Immediately test the water again, and record the nutrient levels. They should read higher than before, but not “off the charts.” If you aren’t getting a very high reading, it is ok to add a little more fertilizer until you have somewhere between 5-10 ppm. Add the fertilizer a little at a time to get the desired level.

6. Set the jar in the sun with the lid off. While it sits, you may do other lessons, or take students on a nature walk.

7. After one-two hours, test the jar again. There should be a lower concentration of available nutrients than an hour before.

8. If you have time, continue to test the jar every hour until the nutrients are all taken up.

9. You may keep the jar over a number of days and continue adding nutrients. Within a day or two there should be a visible increase in algal mass.

Interpreting your results

Nutrients in their available form are taken up very quickly. It is this rapid uptake that causes events such as algal blooms, eutrophication (nutrient overloading), and hypoxia (lack of dissolved oxygen). This is seen on a large scale in the Gulf of Mexico. Nutrients from fertilizers and waste accumulate from streams to rivers, to larger rivers, and eventually to the Mississippi. A massive quantity of nutrients spills from the Mississippi into the Gulf every day, creating a large hypoxic zone where plants can’t grow and fish can’t live. This “Dead Zone” is about the size of New Jersey, and growing.

[1] Plants take up the nitrate (NO3) form. Nitrogen typically enters aquatic systems as ammonia (from animal waste) or nitrite/nitrate (from fertilizers). Once in water, bacteria converts ammonia to nitrite, and nitrite to nitrate. Once in the nitrate form the nitrogen is more available to plants, but because the ammonia and nitrite will be converted into nitrate, they are included in the “total available nitrogen” calculation.